Tracer elements are

Options

A. Micro-elements
B. Macro-elements
C. Radio-isotopes
D. Vitamins

Answer

**Step-by-Step Solution:**

1. **Understanding Tracer Elements**: Tracer elements are specific types of elements that can be used to track processes in biological systems. They are not just any elements but have unique properties that allow them to be traced.

2. **Identifying the Type of Elements**: The question provides four options: microelements, macroelements, radioisotopes, and vitamins. We need to determine which of these categories tracer elements belong to.

3. **Definition of Radioisotopes**: Radioisotopes are isotopes of elements that are radioactive. This means they emit radiation as they decay. This property is crucial for tracing because the emitted radiation can be detected and measured.

4. **Substitution in Metabolic Pathways**: Tracer elements can be substituted for stable isotopes of the same element in biological processes. For example, carbon-14 (C14) can replace carbon-12 (C12) in organic compounds, allowing scientists to trace the movement and transformation of carbon in metabolic pathways.

5. **Examples of Tracer Elements**: Common examples of tracer elements include C14, N15, P32, and S35. These isotopes are widely used in research to study various metabolic processes in plants and other organisms.

6. **Conclusion**: Based on the definitions and examples discussed, tracer elements are best categorized as radioisotopes. Therefore, the correct answer to the question is that tracer elements are radioisotopes.

**Final Answer**: Tracer elements are radioisotopes.

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